Faculty Mentor - Dr. Renato Camata
Yttria-stabilized zirconia (YSZ) is a key material in a variety of emerging technologies. It is used as an electrolyte in solid oxide fuel cells, as a thermal barrier coating in gas turbines, and as a buffer in multi-layer superconductor structures. While YSZ is a very hard material, it has very low fracture toughness. Research has shown that by creating composite YSZ-Al2O3 films, the fracture toughness and other mechanical properties of the films can be dramatically improved. The addition of Al2O3 to the YSZ system has often been achieved through the introduction into the YSZ of Al2O3 microparticles with a broad size distribution. In spite of their superior mechanical properties, these heterogeneous composites present unpredictable effects in their ionic, electronic, and thermal conductivity, often rendering them useless for their primary application.
|Fig. 3 - Schematic of the PLD/NBPLD facility that will be used for creation of YSZ-AL2O3 nanocomposites.|
Recent studies show, however, that tailoring the mechanical properties of YSZ-Al2O3 composites while controlling their conductivity is possible in a nanocomposite for which exquisite control can be exercised over the size, concentration, and dispersion of the Al2O3 nanoparticles. In this project, a student will employ Nanoparticle Beam Pulsed Laser Deposition (NBPLD) to create YSZ films containing size selected Al2O3 nanoparticles (i.e., YSZ-Al2O3 nanocomposites) and investigate their mechanical properties through nanoindentation hardness measurements. Figure 3 shows a schematic of the NBPLD approach, which was pioneered by Camata at UAB and has been recently funded by NSF (DMR#0116098). In this approach, an independent PLD source (NBPLD source in Fig. 3) is fitted with a suitable target (Al2O3 in this case) and used to create a beam of size-selected nanoparticles of the target material using aerosol size classification. The nanoparticle beam is delivered to the deposition substrate while conventional PLD of a second target (YSZ in this case) is used to deposit the matrix material.
Figure 4 shows an AFM image of a single layer of silver (Ag) nanoparticles produced by this method with only the operation of the NBPLD source.
|Fig. 5 - X-ray diffraction of PLD-deposited YSZ film obtained by REU student Jennifer Kirchhoff (2002).|
Nanoparticles obtained had an average diameter of 8.0 nm with a standard deviation of 0.6 nm. Nanoparticle diameters can be tuned in the 1-50 nm size range by simply adjusting a voltage.
During the summer of 2002 REU student Jennifer Kirchhoff demonstrated the deposition of YSZ films using conventional PLD in our facility (Fig. 5). In this project the undergraduate student will use NBPLD and PLD simultaneously to create the desired YSZ-Al2O3 nanocomposites and investigate their mechanical properties through nanoindentation measurements.